The primary goal of this proposal is to examine how the environment and the body's mechanical properties couple with an organism's neural architecture to produce an adaptive behavior. The importance of sensory feedback and direct mechanical coupling between the body and environment will be investigated using lamprey swimming as a paradigm for vertebrate motor behavior. Lampreys cannot produce an effective swimming behavior without these interactions, but the details of how coupling and feedback modulate the spinal central pattern generators (CPGs) to produce the behavior is unknown. The interaction will be examined at three levels: the influence of sensory input on the isolated spinal cord, the feedback loop between the CPGs and the axial musculature, and the mechanical coupling between the muscles and the fluid environment. A mathematical model of the CPG will be constructed to aid in interpretation and generalization of the results to vertebrate locomotion as a whole. This combination of mathematical modeling and experimental tests of different levels of the interaction will allow a broad evaluation of how the vertebrate central nervous system acts together with the body and environment to produce a motor behavior.